1. Technical Field
The present invention relates to an electronic device that receives signals and obtains the current time transmitted from a positioning information satellite such as a GPS satellite.
2. Related Art
The Global Positioning System (GPS) uses GPS satellites (positioning information satellites) that orbit the Earth on known orbits and enables a GPS receiver (GPS device) to determine its own location from these GPS signals. Each GPS satellite carries an atomic clock, and transmits satellite signals that contain time information (satellite time information) representing the time (GPS time) that is kept by the atomic clock. The GPS time is the same on all GPS satellites, and UTC (Coordinated Universal Time) is determined by correcting the GPS time with the UTC offset (currently +15 seconds), which is the difference between GPS time and UTC. The UTC can therefore be determined by receiving a satellite signal and acquiring the GPS time from a GPS satellite, and then correcting the GPS time based on the UTC offset. The UTC offset can be acquired from the received satellite signal, or a specific value that is acquired from local storage could be acquired and used as the UTC offset.
A radio-controlled timepiece that receives satellite signals from GPS satellites to determine the current time is taught in Japanese Unexamined Patent Appl. Pub. JP-A-2003-139875. This radio-controlled timepiece keeps the current local time (local time), stores fixed location information identifying the position of plural fixed locations, such as major cities, correlated to time difference information indicating the time difference at that location, and calculates the current local time using the time information acquired from a satellite signal and the time difference information correlated to the fixed location that is closest to the position of the mobile device determined from the satellite signals. A circular area centered on a particular point is set for each fixed location, and the fixed location assigned to the area associated with the current position of the mobile device is used as the “closest fixed location.”
Japanese Unexamined Patent Appl. Pub. JP-A-2009-128296 teaches an electronic timepiece that receives satellite signals from GPS satellites to determine the current time.
With the radio-controlled timepiece taught in JP-A-2003-139875, the time difference is determined based on whether or not the position of the mobile device is in a circular area. As a result, the current local time could be calculated using incorrect time difference information in regions where there are plural meandering time difference boundaries. For example, the current local time may be calculated using time difference information for a fixed location B neighboring location A even though the user intended for the current local time to be calculated using time difference information for fixed location A.
In this case the user must manually set the current local time. When the user visits the same location the next time, the current local time is again calculated using time difference information not intended by the user (that is, the time difference at location B), and the user must again manually set the current local time. The user must therefore always set the time manually in this location.
This problem is the same with the electronic timepiece taught in JP-A-2009-128296.